Catalysis-tunable Heusler alloys in selective hydrogenation of alkynes: A new potential for old materials

Heusler alloys (X(2)YZ) are well-established intermetallic compound materials in various fields because their function can be precisely adjusted by elemental substitution (e.g., X(2)YZ(1-x)Z(x)'). Although intermetallic compound catalysts started attracting attention recently, catalysis researchers are not familiar with Heusler alloys. We report their potential as novel catalysts focusing on the selective hydrogenation of alkynes. We found that Co2MnGe and Co2FeGe alloys have great alkene selectivity. Mutual substitution of Mn and Fe (Co2MnxFe1-xGe) enhanced the reaction rate without changing selectivity. The substitution of Ga for Ge decreased the selectivity but increased the reaction rate monotonically with Ga composition. Elucidation of these mechanisms revealed that the fine tuning of catalytic properties is possible in Heusler alloys by separately using ligand and ensemble effects of elemental substitution.